This study aims to develop a skull-clearing technique for simple, minimally invasive, and physiological imaging of the brain. We will create a hybrid clearing reagent that combines the advantages of biocompatible aqueous reagents and high-refractive-index organic solvent-based reagents, enabling the clearing of live mouse skulls. Using this technique, we will demonstrate that two-photon live imaging can achieve quality equivalent to the open-skull method in visualizing cellular morphology and neural activity in the brain. Furthermore, we aim to develop a method applicable to thick skull tissues, such as those of aged mice and primates, to elucidate the spatiotemporal dynamics of brain-border macrophages.